Conventionally, in a cutting insert including a major cutting edge for cutting a workpiece and a flat cutting edge for smoothing the surface of the workpiece produced by the cutting, a minor cutting edge having a larger peripheral cutting edge angle than the major cutting edge is formed between the major cutting edge and the flat cutting edge from the viewpoint of damage reduction of a cutting edge. For example, Japanese Unexamined Patent Publication No. 2008-6579 discloses a cutting insert in which the angle formed between a major cutting edge and a flat cutting edge is 45°, and an intermediate cutting edge 11 (minor cutting edge) having a larger peripheral cutting edge angle than the major cutting edge is formed between the major cutting edge and the flat cutting edge.
However, the thrust force on the minor cutting edge during cutting increases in these cutting inserts. Therefore, vibration (chatter phenomenon) is likely to occur during the cutting, and the quality of a finished surface may deteriorate.
Also, it has been difficult for these cutting inserts to conform to a plurality of cutting conditions from general feed to high feed (high feed rate cutting).